1. Field of the Invention
The invention relates generally to the field of oil and gas well services. More specifically, the present invention relates to an apparatus that orients a tool into a desired position while the tool is in a deviated wellbore.
2. Description of Related Art
When downhole tools, including perforating guns, are used in slanted or deviated wellbores it is often important that the tool be in a specific radial orientation. For example, orienting perforating guns in deviated wells enables the well operator to aim the shaped charges of the perforating gun at specific radial locations along the circumference of the wellbore. This is desired because the potential oil and gas producing zones of each specific well could exist at any radial position or region along the wellbore circumference. Based on the presence and location of these potential producing zones adjacent a deviated well, a well operator can discern a perforating gun orientation whose resulting perforations result in maximum hydrocarbon production.
Information relevant to attempts to orient downhole tools, including perforating guns, can be found in U.S. Pat. Nos. 4,410,051, 4,438,810, 5,040,619, 5,211,714, 4,637,478, 5,603,379, 5,964,294. However, each of these references suffers from one or more of the following disadvantages. Some of the devices described in these references position a perforating gun such that only downward perforations are possible, others obstruct the path of the some of the shaped charges located on the perforating gun, while others are attached to the exterior of the perforating gun which can make handling of the tool inside of a wellbore more cumbersome.
Daniel et al, U.S. Pat. No. 4,410,051 discloses a system for orienting a perforating gun to be used in wells having multiple tubing strings. The apparatus of Daniel et al. ""051 consists of a plurality of subassemblies connected end to end. Situated in one of the subassemblies is an eccentric weight sub that contains a weight positioned asymmetric to the longitudinal axis of the housing. Connected to the bottom of the eccentric weight sub is the alignment joint sub which is used to align the bottom portion of the housing with outlets of the perforating gun. In Daniel et al. ""051 the perforating gun section of the apparatus is disclosed as being below the eccentric weight sub. Wilkinson, U.S. Pat. No. 4,438,810 and Jordan et al., U.S. Pat. Nos. 5,040,619 and 5,211,714 also disclose the use of an eccentrically weighted sub attached to a perforating gun to rotate the perforating gun inside of a deviates wellbore.
George, U.S. Pat. No. 4,637,478 involves a gravity oriented perforating gun for use in slanted wells comprised of one or more segments or subs, where each sub contains a center of gravity movement means which is a window that is cut out of the sub wall to alter the sub symmetry. Because it is asymmetric, the sub will rotate until the heavier portion of the sub circumference is below the lighter portion of the sub circumference.
Henke et al., U.S. Pat. No. 5,603,379, involves an apparatus for connecting and orienting perforating guns in a deviated well bore. The orientation aspect of the device consists of a fin longitudinally connected to the body of the perforating gun that positions the gun off center in the casing so that gravity will position the gun body at the bottom of the casing. Because of the positioning aspect of Henke ""379, the perforations are generally directed into a downward trajectory. Vann, U.S. Pat. Nos. 4,194,577 and 4,269,278 also disclose a perforating gun including longitudinal disposed fins on the gun outer circumference which act to direct the perforating charges in a downward pattern.
Edwards et al., U.S. Pat. No. 5,964,294, discloses a downhole tool for use in a deviated well constructed to rotate in response to a moment applied at its axis. The tool includes ballast chambers filled with a flowable ballast material to produce a gravitational force for rotating the tool. The ballast chambers are formed on the inner diameter of the loading tube assembly. The flowable ballast material consists of a high density metal such as tungsten or depleted uranium. Alternative embodiments include a multiple segmented tool where each tool has offset centers to produce rotation of the tool.
Therefore, there exists a need for a system that orients perforating guns in deviated wellbores where the shaped charges of the perforation gun can be directed in any radial orientation, a system that cooperates with a perforating gun having any shot pattern without affecting the shot pattern, and a system that is integral within the perforating gun.
One embodiment of the present invention discloses a system and method for orienting downhole tools, including perforating guns, into a specified orientation, while the tool is inside of a deviated or slanted wellbore. The tool comprises a perforating gun having a substantially cylindrical gun body with an inner and an outer diameter. Disposed within the gun body is a gun tube also with an inner and an outer diameter. The gun tube contains at least one shaped charge. Attached to the outer surface of the gun tube is a weight. Each weight has apertures formed therethrough that are aligned with each shaped charge so that the shot performance of each shaped charge is not affected by the attached weight during detonation. The attached weight can be equal to or less than the length of the gun tube.
A method of aligning a perforating gun in a deviated wellbore comprises adapting a weight for attachment to the outer surface of a gun tube having one or more shaped charges. Radial locations along the weight are identified that coincide with the location of each shaped charge. Apertures through the weight are formed at each radial location. The weight is attached to the outer surface of gun tube such that the apertures are coaxially aligned with each shaped charge. The gun tube is placed into the gun body of a perforating gun, and the perforating gun containing the gun tube is inserted into the deviated section of a wellbore. When the rotation of the gun body caused by the Earth""s gravitational force upon the eccentric weight has ceased, the shaped charges are ready to be detonated.
The method also envisions receiving coordinates where perforations are desired within the wellbore. The weight is then strategically situated on the gun body such that rotation of the gun body caused by the Earth""s gravitational force upon the weight orients the gun body so the shaped charges are aimed at the coordinates.